clk/qcom: fix rcg divider value

The RCG divider field takes a value of (2*h - 1) where h is the divisor.
This allows fractional dividers to be supported by calculating them at
compile time using a macro.

However, the clk_rcg_set_rate_mnd() function was also performing the
calculation. Clean this all up and consistently use the F() macro to
calculate these at compile time and properly support fractional divisors.

Additionally, improve clk_bcr_update() to timeout with a warning rather
than hanging the board, and make the freq_tbl struct and helpers common
so that they can be reused by future platforms.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>